1. Field of the Invention
This invention relates to a system and method for treating flowing water systems using a high voltage discharge to generate plasma and using the ozone by-product from the high voltage generation, particularly useful in treating cooling tower or other recirculating or closed-loop systems.
2. Description of Related Art
Anthropogenic water systems are critical components commonly found in most of the world's energy producing facilities, industrial and manufacturing plants, hospitals, and other institutional complexes and buildings. These systems consume around 700 billion gallons of water annually with a cost of $1.8 billion in make-up water and sewage handling costs alone. All of these anthropogenic water systems require some form of treatment, either chemical or non-chemical, to control the build-up of scale, biofilm and other corrosion by-products on the important heat transfer surfaces that are necessary for efficient system operation.
For water systems involving heat exchange, such as cooling towers and boilers, effective treatment to remove these contaminants and to prolong the amount of time before the systems are re-contaminated can save significant amounts of money. An effective and thorough treatment may save costs for labor and treatment chemicals by reducing the frequency of periodic treatments or reducing the amount of chemicals needed for routine maintenance and/or periodic treatments. Such a treatment may also save on energy costs through the operation of clean heat exchange surfaces. Fouling of heat exchange surfaces costs U.S. industry hundreds of millions of dollars every year and is directly related to an increase in energy consumption of almost 3 quadrillion Btus (quads) annually.
To maximize the water usage and minimize waste, many of these systems employ a series of chemical treatments that protect the system against scaling, biofilm formation, and corrosion. These chemical treatments allow the water to be reused and recycled a number of times before it becomes necessary to discharge the water and replace it with fresh water. Increasing the duration for which the water may be circulated significantly reduces the amount of water that is discharged to the sewage system and minimizes the amount of make-up water that is needed to replace the bleed off. However, many chemical treatment compositions and methods may damage the components of the water system being treated as the chemicals used are highly corrosive. There is also an environmental down side to harsh chemical treatments, including growing concern over the formation of toxic disinfection-by-products such as trihalomethanes, haloacetonitriles, and halophenols that have been identified in the discharge water being released into the environment. It is estimated that there are 536 billion pounds of water treatment chemicals discharged annually as a result of cooling tower treatments, which may impact a variety of species living in or near areas and water-ways receiving the discharge or bacterial components of sewage treatment plants receiving the discharge.
In an attempt to minimize the environmental impact associated with some chemical treatments, many water treatment companies, and more importantly their customers, are looking to use non-chemical based water treatment technologies to maintain the performance of their systems. There are currently about 30 non-chemical treatment devices or water conditioning technologies that are commercially available for use in both commercial and residential water systems. These systems can be divided into three categories: (1) Indirect chemical producers that use a benign or safe chemical additive such as air or salt to produce the biocide. These systems include ozone generators and electrochemical hypochlorite generators and mixed oxidant generators. (2) Direct chemical producers that generate the active chemical species from direct interaction on the water. These devices use mechanical processes, such as hydrodynamic cavitation or sonic cavitation, to produce hydroxyl radicals along with localized areas of high temperatures and pressures in the water. Other types of devices that would fit into this category are ultraviolet light systems. (3) Electrical and Magnetic devices, including plasma generation, use induced electrical and magnetic fields to induce ion migration and movement that can result in cell death through electroporation, or ion cyclotron resonance effects within the cell wall. Out of all of these technologies the electrical and magnetic devices are the most common; however, they are the technologies that have the least rigorous scientific support. The direct and indirect chemical approaches have more scientific credibility; however, this greater understanding may have limited their potential applications and hence they have not been able to capture a larger portion of the market share.
The application of high voltage discharge and generating plasma within water is known in the prior art. For example, an article published by B. R. Locke et al. (Ind Eng. Chem Res 2006, 45, 882-905) describes electrode configuration and geometry, the pulsed arc vs. pulsed corona, and the chemical species that are formed during an electrohydraulic discharge and non-thermal plasma in water discharge process. The article addresses many of the fundamental issues related to using this technique for water treatment, but it fails to address the practical applications related to water treatment in an industrial, commercial, or residential environment, especially related to the need for multiple ground points to minimized the effect of the electromagnetic radiation released into the water and surrounding atmosphere.
It is also know to use ozone gas to treat water. For example, in an article by Gupta et al. (S. B. Gupta, IEEE Transactions on Plasma Science, 2008, 36, 40, 1612-163) the use of an advanced oxidation process resulting from pulsed discharges in water is described. The process described by Gupta uses oxygen gas or ozone gas supplied into the discharge reactor from secondary independent sources (and not from the high voltage generator). They also report that system output and performance is highly dependent on solution conductivity. For systems where water conductivity can be high, such as in cooling tower and closed loop applications, higher voltage discharges are needed and this in turn creates problems with increased electromagnetic radiation.
There are also several prior art patents or published patent applications that address plasma generation for various purposes, including water treatment or purification, such as U.S. Patent Application Pub No. 2009/0297409 (generation of flow discharge plasmas at either atmospheric or higher pressures), U.S. Patent Application Pub No. 2006/0060464 (generation of plasma in fluids, in particular formed within the bubbles generated and contained in an aqueous medium), U.S. Pat. No. 6,558,638 (using high voltage discharge to treat liquids, while incorporating a gas delivery means for generating bubbles in the discharge zone), and U.S. Patent Application Pub No. 2010/0219136 (pulsed plasma discharge to treat fluid such as water at a flow rate of 5 gpm while consuming only 120-150 Watts of power).
The prior art teaches that high voltage discharges in water can generate chemically active species, exhibit physical effects, and control water chemistry. However, the known prior art does not address the how to apply this technology of using plasma discharge to treat larger volumes of flowing water in an industrial, commercial or residential setting over longer periods of time without damaging other components of the water system, including the controllers and monitors that are needed for scale and corrosion control, blowdown, and water conservation measures.